DE102015222589A1 - Generating a volume image of an elongated examination object - Google Patents

Abstract

The invention relates to a tomography system (R), which is prepared for the following: Performing a first scan along a first helix-segment-shaped trajectory section (BA1) and a second scan along a second helix-segment-shaped trajectory section (BA2). In the first scan, a first data set (DS1) and in the second scan a second data set (DS2) are obtained and from the two data sets (DS1, DS2) a fused three- or four-dimensional data set (DS12) is generated, which is used for a reconstruction of a volume image (DS2). VB) without Teilumlaufartefakt is sufficiently complete, in each case taken on their own both the first (DS1) and the second (DS2) data set for a reconstruction of a volume image (VB) without Teilumlaufartefakt is too incomplete. The invention also relates to a corresponding method (100) for operating a tomography system (R).

Description

The invention relates to a tomography system which is prepared to perform a first scan along a first helix-segment-shaped trajectory section and a second scan along a second helix-segment-shaped trajectory section. The first scan will acquire a first record and the second scan a second record.

Moreover, the invention relates to a corresponding method for operating a tomography system.

A data record is here preferably understood to be a data record of a volume scan, from which a complete three- or four-dimensional volume image can be reconstructed. A data set of a volume scan comprises the acquired image data of the associated projection image for each projection angle used. A four-dimensional volume image is usually understood to mean a sequence of at least two three-dimensional volume images which follow one another in terms of time. In this case, a first of the at least two three-dimensional volume images, for example, a flooding phase and a second of the at least two three-dimensional volume images, for example, an outflow phase. The tomography system can be, for example, an x-ray tomography system or a fluorescence tomography system.

Particularly in diagnostics and therapy, ever higher demands are placed on the performance of medical devices. This is in particular the goal of avoiding health hazards and personal injury as a result of incorrect diagnosis or treatment.

The DE 10 2006 040 934 A1 describes a method for presenting arteries and / or veins of a vascular system by means of a C-arm biplane system comprising two C-arms. During a filling run, a sequence of X-ray images from different projection angles is recorded for each C-arm. The X-ray images of the filling run from the first and second C-arcs from an arterial phase are combined into a first data set. The reconstruction to a three-dimensional image data set can be carried out before the combination of the data of the X-ray images of the two C-arms or on the data set of the extracted arterial vascular system.

With known C-arm angiography systems, it is not possible to detect an entire body or large parts of a body of a normal-sized adult by means of a single scan trajectory. For with known C-arm tomography systems, cable feeds for the C-arms limit the rotational angle span (about the orbital axis) of the beam source-detector pair of the respective C-arm to approximately 400 °.

It is an object of the present invention to provide a tomography system and method for operating a tomography system that overcomes this design problem of conventional tomography systems.

This object is achieved according to the invention by a tomography system which is prepared to perform a first scan along a first helix-segment-shaped trajectory section and a second scan along a second helix-segment-shaped trajectory section. The tomography system is prepared to obtain a first data set during the first scan and a second data set during the second scan and to generate a fused data set from the two data sets which is sufficiently complete for reconstructing a three- or four-dimensional volume image without a partial circulation artifact. Each taken alone, both the first and the second data set for a reconstruction of a volume image without Teilumlaufartefakt is too incomplete.

The method according to the invention for operating a tomography system comprises the following actions. A first scan along a first helix-segment-shaped path curve section and a second scan along a second helix-segment-shaped path curve section are performed. During the first scan, a first data set and the second scan, a second data set is obtained, in each case taken on their own both the first and the second data set for a reconstruction of a volume image without Teilumlaufartefakt is too incomplete. From the two data sets, a fused data set is generated which is sufficiently complete for a reconstruction of a three- or four-dimensional volume image without partial circulation artifact.

One concept of the present invention may be seen in that the tomography system is prepared to generate from the two data sets a fused data set which is sufficiently complete for reconstruction of a three- or four-dimensional volume image without partial circulation artifact, taken both alone the first and the second data set for a reconstruction of a volume image without partial circulation artifact is too incomplete. For example, each rotation angle span can be limited to 180 ° or 100 ° for the individual scan, without having to accept partial revolution artifacts to have to. This results (in particular with regard to the cable feeders for each individual C-arm) considerable structural advantages. From the fused data set, a three- or four-dimensional image can be reconstructed by means of a known reconstruction method (for example by means of a filtered rear projection method according to Feldkamp, Davis, Kress). The reconstructed image may be two-, three-, or four-dimensional, with its dimension at most as large as the dimension of fused data set. Typically, both trajectories have an identical shape (but typically with a rotational angle difference and / or an orbital axis direction offset). Typically, the second helical segment-shaped trajectory is arranged concentrically to the first helix segment-shaped trajectory. Regardless, it is also preferred if a radius of the first helix-segment-shaped trajectory curve is the same size as a radius of the second helix-segment-shaped trajectory curve. There are also conceivable applications in which it is advantageous if the slope of the helix-segment-shaped trajectories is zero. In the degenerate case, the helix-segment-shaped trajectories can therefore be circular segment-shaped.

One embodiment provides that the first helix-segment-shaped path curve section extends over a first rotation angle span and the second helix segment-shaped path curve section extends over a second rotation angle span, the sum of the first and the second rotation angle span being 360 °. Here, a minimum rotational angular position of the second helix-segment-shaped trajectory section is offset from the minimum rotational angular position of the first helix-segment trajectory section in the rotational direction by the first rotational angular span. Alternatively, the minimum rotational angular position of the first helix-segment-shaped trajectory section relative to the minimum rotational angular position of the second helix-segment trajectory section can be offset in the direction of rotation by the second rotational angular span. From the data sets of two scans, which were performed over mutually complementary rotation angle spans of 180 °, a fused data set can be generated, from which a complete volume image without partial circulation artifact can be reconstructed.

This is especially true if both scans are run as Large Volume Scan. In a large volume scan, a center of a sensor surface of the detector relative to a central beam of the beam of the beam source is shifted by half a detector width in the direction of rotation or opposite to the direction of rotation. As a result, a diameter of the evaluable recording area in the direction of rotation is increased approximately by a factor of two.

A further embodiment provides that the first helix-segment-shaped path curve section extends over a first rotation angle span and the second helix-segment-shaped path curve section extends over a second rotation angle span RS _C2 , wherein the first rotation angle span RS _C1 is calculated as follows: RS _C1 = 180 ° + SW - RS _C2 .

The second rotation angle range RS _C2 is mindestes half as large as a width SW of a beam angle in the rotational direction. A minimum rotational angular position of the second helix-segment-shaped trajectory section is offset from the minimum rotational angular position of the first helical segment trajectory section in the rotational direction by the first rotational angular span. Alternatively, the minimum rotational angular position of the first helical segment-shaped trajectory section relative to the minimum rotational angular position of the second helical segment trajectory section is arranged offset in the rotational direction by the second rotational angular span. From the data sets of two scans, which are performed on mutually adjacent rotation angle spans, a fused data set can be generated, from which, as in a short scan, a complete volume image can be reconstructed without partial circulation artifact. For a short scan, it is assumed that a center of a sensor area of the detector is arranged in a central ray of the beam of the beam source.

In order to perform a large volume scan, it is also possible that the rotation angle spans for the first and second scans are identical and each comprise 90 ° plus one half of the beam angle, with the sensor surface being shifted in the opposite direction between the two scans Center of a sensor surface of the detector relative to a central beam of the beam of the beam source is shifted by half a detector width in the opposite direction.

Special benefits arise when the tomography system is prepared to obtain a first part of the second data set having a second radiation spectrum that differs from a first radiation spectrum with which a first part of the first data set is obtained. A further development provides that the first part of the first data record comprises the entire first data record and the first part of the second data record comprises the entire second data record. An alternative development provides that the tomography system is prepared to obtain a remaining part of the first data set with the second radiation spectrum and a remaining part of the second data set with the first radiation spectrum. If, for generating the second radiation spectrum, a different anode voltage and / or an anode material is used than for generating the first radiation spectrum, density measurements can be carried out, for example. In this embodiment, the first data set typically comprises the projection image data of two helix-segment-shaped path segments, the first of which is traversed by the first radiation spectrum and the second by the second radiation spectrum, the second data set also comprising the projection image data of two helix-segment-shaped path segments, the first of which is traversed with the second radiation spectrum and the second with the first radiation spectrum. By exchanging the data of the second helix segment-shaped path section between the two data sets, a first complete data set for the first radiation spectrum and a second complete data set for the second radiation spectrum can be obtained.

It is also advantageous if the first data record is recorded only on first helix-segment-shaped trajectory sections which run in a first direction of rotation. This has, inter alia, the advantage that a small or a large perpendicular bisector of a first (rectangular) sensor surface of the first detector can be aligned parallel to the first helix segment-shaped trajectory section without this orientation needing to be changed during the stepwise passage of Helixwindungen. During the helix turns, the sensor surface does not need to be rotated about the central ray of the beam of the beam source, so that a yaw angle between the small and large bisectors of the first sensor surface and the first helical segment trajectory portion is zero degrees when recording the first data set.

Alternatively or additionally, the second data set is recorded only on second helix-segment-shaped trajectory sections which extend in a direction of rotation which is opposite or rectified to the first direction of rotation. If the first data set is obtained only on first helical segment-shaped trajectory sections extending in a first rotational direction and the second data set is obtained only on second helical segment trajectory sections extending in a rotational direction opposite to the first rotational direction, this may help to influence the first data set by a beam source, which is provided for the acquisition of the second data set and / or help to avoid influencing the second data set by a beam source, which is provided for the acquisition of the first data set.

It is particularly advantageous if the first scan is recorded when a perpendicular bisector of a first sensor surface of the first detector is aligned parallel to the first helix segment-shaped trajectory section. Alternatively or additionally, the second scan can be recorded if a perpendicular bisector of the second sensor area of the second detector is aligned parallel to the second helix-segment-shaped trajectory section. As a result, the sensor surfaces are aligned so that their use for the scan according to the invention is optimal. An even better use of the respective sensor surface can be achieved if the sensor surface of the respective detector has the shape of a parallelogram whose internal angle is matched to the pitch of the helix-segment-shaped trajectory section on which the associated beam source is active.

Regardless, the tomography system may be prepared to perform the first scan when a center of a sensor surface of the first detector is shifted from the central beam of a beam of the first beam source by half a detector width in the direction of rotation or half a detector width opposite to the direction of rotation. Alternatively, the tomography system may be prepared to perform the first scan when a center of a sensor area of the first detector is shifted from a central beam of a beam of the first beam source by a half detector width in a direction of the first helix segmental trajectory section. Each of these measures is suitable to increase a diameter of an evaluable recording area in the direction of rotation.

Alternatively or additionally, an extension of the field of view in the direction of rotation can also be achieved by means of a reduction of the source-to-sensor distance SID (source to image distance).

Depending on the tomography system used, it may be expedient for a minimum rotational angular position of the second helix-segment-shaped trajectory section to be spaced apart from a minimum rotational angular position of the first helix-segment-shaped trajectory section in orbital alignment. This measure may contribute to a device required for the first scan not disturbing (physically obstructing) the device required for the second scan and / or requiring a device necessary for the second scan , none Disturb device that is required for the first scan. This may be particularly relevant if the two scans are performed synchronously (for example by means of one C-arm each) in a biplane tomography system.

It is particularly preferred for the tomography system for the first scan to have a first beam source and a first detector associated with the first beam source, and for the second scan a second beam source and a second detector associated with the second beam source. Typically, a distance of the first beam source to the first detector remains constant, while the first detector is guided along the helix-segment-shaped first trajectory around the orbital axis. This also applies to a distance between the second beam source and the second detector.

If the tomography system is a monoplane tomography system, the second scan is performed with the same detector as the first scan, before or after the first scan.

The first beam source and the first detector may be attached to a common movable carrier, for example a same first C-arm or to different movable carriers, for example to a respective robotic arm. The same applies to the second beam source and the second detector. Even both beam source-detector pairs may be attached to a common movable carrier, for example a same C-arm. Optionally, an image intensifier can be connected to the first detector. This also applies to the second beam source and the second detector. An independent option provides that the first detector comprises an image intensifier and / or the second detector comprises an image intensifier. The concepts according to the invention can also be applied to a tomography system with more than two beam sources, for example to a triplan or quattroplan tomography system.

The invention is explained in more detail with reference to the accompanying drawings, in which:

1 schematically a biplane tomography system according to the invention,

2 1 schematically shows a scan of a first embodiment of a biplane tomography system,

3 schematically with respect to a fully reconstructible volume, optionally an arrangement of two beam source-detector pairs or two positions of a same beam source-detector pair at two different times,

4 schematically a data flow of a tomography system according to the invention,

5 schematically a scan of a second embodiment of a biplane tomography system,

6 schematically a scan of a third embodiment of a biplane tomography system,

7 schematically a scan of a fourth embodiment of a Biplan-Tomographieanlage, and

8th schematically a flow of a method for operating a tomography system.

The embodiments described in more detail below represent preferred embodiments of the present invention.

In the 1 Biplan tomography system R shown has a first C1 and a second C2 C-arm and a patient support PA. A first beam source Q1 and a first detector RD1 are attached to the first C-arm C1. A second beam source Q2 and a second detector RD2 are attached to the second C-arm C2. To perform a cross-scan on an object ZO to be examined, the first C-arm C1 performs an orbital rotation RO about an orbital axis OA, while the second C-arm C2 also synchronously performs an orbital rotation RO about the same orbital axis OA. At the same time, the patient rest PA is moved along the orbital axis OA. This is typically done at a constant velocity in orbital axis direction z. In the orbital rotation RO of the first C-arm C1, the (imaginary) plane in which the first C-arm C1 is located usually remains unchanged. The same applies to the second C-arm C2. In principle, however, it is also conceivable that, alternatively or additionally, both C-arms are moved along the orbital axis OA during the scan. If the tomography system R is a monoplane tomography system, ie only a C-arm C1 is present, the second scan is performed with the same detector RD1 as the first scan, namely before or after the first scan. Incidentally, the same concepts and considerations are applicable as are known and / or described for a biplane tomography system.

The 2 shows a first rotation angle span RS _C1 in which the first detector RD1 is positionable, and a second rotation angle span RS _C2 in which the second detector RD2 is positionable. The first detector RD1 performs a zigzag movement over the entire first rotation angle span RS _C1 of 180 °. Each time the first detector RD1 ends one or the other of the first Rotation angle span reaches RS _C1 , he changes, together with the beam source Q1, which is associated with him, the rotation direction RR1, RR2. In relation to the object ZO to be examined, the first detector RD1 thereby passes through helix-segment-shaped trajectory sections BA1 with alternating rotational directions RR1, RR2. The same applies to the second detector RD2. Each time the second detector RD2 reaches one or the other end of the second rotation angle span RS _C2 , it alternates the rotation direction RR1, RR2 with the beam source Q2 associated with it. In relation to the object ZO to be examined, the second detector RD2 thus also passes through helix-segment-shaped trajectory sections BA2 with alternating rotational direction RR1, RR2.

By periodically juxtaposing the helical segment-shaped trajectory sections, scans of any length are possible. In this case, each of the two beam source-detector pairs Q1 / RD1, Q2 / RD2 each performs a zigzag movement over a rotation angle span RSC1 or RSC2. The beginning of the period T of the back and forth movement of the second beam source-detector pair Q2 / RD2 may coincide with the beginning of the period of the back and forth movement of the first beam source-detector pair Q1 / RD1 or (as in the example of FIGS 6 shown) with respect to the beginning of the period of the back and forth movement of the first beam source-detector pair Q1 / RD1 be offset in time by a fraction (for example, by one half) of the period T. This applies to all embodiments described here.

In the embodiment of the 2 For example, the first beam source Q1 generates a first radiation spectrum in the first rotation direction RR1 and a second radiation spectrum in the second rotation direction RR2. The second beam source Q2 generates the first radiation spectrum in the second rotation direction RR2 and the second radiation spectrum in the first rotation direction RR1. In this figure, scan sections in which the first radiation spectrum is used are framed by solid lines and scan sections in which the second radiation spectrum is used are framed by dashed lines. This also applies to the following figures. The 2 illustrates that over the entire range scanned in orbital axis direction z, over 360 ° each angle is scanned at the intended angular resolution (of, for example, 1 °). This applies to both the first and the second radiation spectrum.

Alternatively, one in the 2 to 7 not explicitly shown constellation possible in which the second beam source Q2 generates the first and second radiation spectrum respectively in the same rotation direction RR1, RR2, as the first beam source Q1, so the first radiation spectrum in the first rotation direction RR1 and the second radiation spectrum in the second rotation direction RR2 , This also scans each angle with the intended angular resolution (of, for example, 1 °) for each of the two radiation spectra over 360 °. This applies to the entire area scanned in orbital axis direction z.

The 3 Figure 3 shows the boundaries of a fully reconstructible volume RV and an array of two beam source-detector pairs Q1 / RD1, Q2 / RD2 of a biplane tomography system R and their pyramidal beam cones SK1, SK2. Optionally, the arrangement may also be considered as positions of a single beam source-detector pair Q1 / RD1 at two different times. The first beam cone SK1 intersects the lateral surface MF of the completely reconstructable volume RV both on the inlet side and on the outlet side.

As the minor figure illustrates, it follows from the step angle set and the center angle set that the exit area AF in the direction of rotation RR1 is three times as wide as the entrance area EF. The extension of the exit surface AF in the orbital axis direction OAR is calculated as 4 · ZR · sin (SW / 2), where ZR denotes the cylinder radius of the fully reconstructable volume RV. In the in the 3 In the embodiment shown, the isocenter lies on an iso-axis IA, which coincides with the orbital axis of the tomography system R and with the axis of symmetry of the cylindrical, completely reconstructable volume RV. Depending on the specific embodiment selected, when designing a scan scheme, the difference in the dimensions of the entrance surface EF and the exit surface AF must be taken into account. In order to avoid a partial circulation artifact, with the intended angular resolution (of, for example, 1 °) over a rotation angle range of at least 180 °, each location of the lateral surface MF of the beam cone SK1, SK2 of at least one of the two beam source detector pairs Q1, Q2 must be at least one Position of the beam source-detector pair Q1 / RD1, Q2 / RD2 are irradiated. The rotation angle range can also not be contiguous, with diametrically opposed rotation angle layers are not double, but only easy to count.

The 4 shows a fuser FU for generating a fused data set DS12 from the first DS1 and second DS2 data set and a reconstructor RE for generating a three- or four-dimensional volume image VB. In the simplest case, the fusioner FU serves a purely aggregative union of the first DS1 and the second DS2 data record (for example by means of a Union query). The reconstructor RE generates this three- or four-dimensional volume image VB from the fused data set DS12 by means of a known reconstruction method (for example by means of a filtered back projection method according to Feldkamp, Davis, Kress).

Also in the embodiment of the 5 Both of the beam source-detector pairs synchronously perform zigzag movements over a rotation angle span of 180 ° each. However, the first beam source Q1 is active here only in a first rotational direction RR1 and the second beam source Q2 is active only in a second rotational direction RR2, which is opposite to the first rotational direction RR1.

An embodiment not shown in the figures provides that both beam source detector pairs synchronously perform zigzag movements over a rotation angle span of 180 °, wherein both beam sources Q1, Q2 are active in a same direction of rotation RR1 or RR2.

The 5 shows that over the entire range, which is scanned in orbital axis direction z, over 360 ° every angle is scanned with the provided angular resolution (of for example 1 °). In this case, typically the same radiation spectrum is always used.

In this case, the respective detector can always remain in a position in which a small MSk or a large MSg perpendicular bisector of the (rectangular) sensor surface SF1, SF2 of the respective detector with (the slope) of the helix segment-shaped trajectory sections BA1 during such periods is aligned, in which him associated beam source Q1, Q2 is active (ie along the "leading" trajectory sections). This also applies to the embodiments described below. The alignment of a mid-perpendicular MSk, MSg of the sensor surface SF1, SF2 with (the slope) of the helix-segment-shaped trajectory sections BA1 avoids unnecessary overlapping of neighboring scan sections and thus improves dose efficiency and optimizes acquisition speed. If the beam sources Q1, Q2 are inactive (ie along the "returning" trajectory sections) the respective detector RD1, RD2 for data acquisition is not needed, so it can remain rotated around the central beam ZS, as it is for the subsequent data acquisition along the "leading" Trajectory sections is appropriate.

In the embodiment of the 6 The two beam source-detector pairs synchronously perform zigzag movements over a rotation angle _span RS _C1 , RS _C2 of 180 °, respectively. Here, both beam sources Q1, Q2 are active in a first rotational direction RR1, while both beam sources Q1, Q2 are not active in a second rotational direction RR2, which is opposite to the first rotational direction RR1. The figure shows that over the entire range, which is scanned in orbital axis direction z, over 360 ° each angle is scanned with the intended angular resolution (of, for example, 1 °). In this case, typically the same radiation spectrum is always used. For the embodiment of 6 For example, the offset of the beginning of the period T of the back and forth movement of the second beam source-detector pair Q2 / RD2 from the beginning of the period of the back and forth movement of the first beam source-detector pair Q1 / RD1 is optional.

The 7 shows an embodiment with a merged helix short scan. Here, each of the two beam source-detector pairs performs zigzag motions over a rotation angle span of 1/2 * (180 ° + SW), where SW denotes a beam angle of the beam sources Q1, Q2. In a short scan for all locations (pixels, voxels) located within a convex hull of the trajectory (trajectory), partial rotation artifacts should be avoided, the total rotation angle of the central rays ZS of the two radiation sources Q1, Q2 must be at least 180 for each of these locations ° plus beam angle (in plane of rotation, ie perpendicular to the orbital axis) total. This beam angle can also be referred to as a fan angle. For example, if the beam angle is 20 °, each of the two rotation angle ranges RS _C1 , RS _{C2 has} a width | RS _C1 |, | RS _C2 | of 100 °. However, both beam sources Q1, Q2 are active in a first rotation direction RR1 but active in a second rotation direction RR2, which is opposite to the first rotation direction RR1. For the embodiment of 7 the shown rotation of the detector RD1, RD2 around the central beam ZS is optional.

The figure shows that over the entire range, which is scanned in orbital axis direction z, over 180 ° plus beam angle SW of, for example, 20 °, each angle is scanned at the intended angular resolution (of, for example, 1 °). In this case, typically the same radiation spectrum is always used.

In all embodiments, the scan can optionally be performed with a monoplane system or with a biplane R device. When the scan is performed with a monoplane system, it is particularly efficient if the helix-segment-shaped path curve sections BA1 of the first rotation angle span RS _C1 are scanned in a first operation and the helix-segment-shaped path curve sections BA2 of the second rotation angle span RS _C2 are scanned in a second operation ( for example, during a retraction of the patient support PA).

This in 8th illustrated method 100 for operating a tomography system R comprises the following actions. A first scan along a first helix-segment-shaped trajectory section BA1 and a second scan along a second helix-segment-shaped trajectory section BA2 are performed. During the first scan, a first data set DS1 and a second data set DS2 are obtained during the second scan, with each of the first DS1 and the second DS2 data set being too incomplete for a reconstruction of a volume image VB without a partial circulation artifact. From the two data sets DS1, DS2 a fused data set DS12 is obtained, which is sufficiently complete for a reconstruction of a three- or four-dimensional volume image VB without partial circulation artifact.

With the present invention, a new trajectory is proposed which enables a helical acquisition by means of a biplane system R. By a juxtaposition of helixsegmentförmigen trajectory sections (to which the 2 and 5 to 7 Illustrate embodiments) scans of any length are possible. This acquisition may be combined with one or more displacements of the detector or detectors RD1, RD2 such that a diameter of the reconstructible region is doubled to twice that. In this way, volume images VB of arbitrarily long volumes can be generated in a structurally advantageous manner by means of a monoplan or biplane C-arm tomography system R.

A preferred embodiment of the method according to the invention 100 provides that both planes of a biplane tomography unit R are rotated synchronously to collectively achieve a continuous helix acquisition. The two levels rotate synchronously forward and backward again and again. As a result, each individual plane scans a reversing helix whose rotation angle _span RS _C1 , RS _{C2 is} limited. This results in a double scan, which includes two helices Ha, Hb with mutually opposite winding direction (mutually opposite direction of rotation). With the data acquired by means of the double scan, fast and dose-efficient acquisition and generation of a volume image VB is possible by means of known reconstruction algorithms.

It is also possible to realize dual-energy scans by setting different anode voltages for both planes and at the inflection points of the respective trajectory reversing the anode voltages of the beam sources Q1, Q2 (at least in terms of value) between the planes. This results in two complete helices H1, H2 for each one anode voltage. For the value-wise interchanging of the anode voltages, the following alternatives exist in principle: changing the voltage of a voltage source which is assigned to the respective beam source Q1, Q2 (fixed); Exchanging the assignment of the two voltage sources to the two beam sources Q1, Q2 by means of a cross-switch; Swapping the assignment of the two beam sources (C-arms) to the two levels.

In order to avoid self-collision, the two planes can be offset in the direction of rotation RR1, RR2 and / or along the orbital axis direction z. Alternatively, the trajectory can also be realized on monoplan systems by taking the two partial trajectories in succession.

In some embodiments of the tomography system R according to the invention parts of the object ZO to be examined are recorded multiple times by the double scan. This redundancy may be used to achieve, for example, one or a combination of the following objectives: reducing noise, compensating for motion, determining density information by switching one or more radiation parameters (for example, to generate a complete dual source tomogram), zooming in a pitch of helical turns (for example, from 22.5 cm to 45 cm). With the same radiation intensity, a faster feed is possible with the latter measure (under otherwise identical conditions), whereby a recording time can be reduced and a dose efficiency can be improved.

For all embodiments applies that the feed either by movement of the object to be examined ZO (for example by means of the patient support PA) and / or by movement of the beam source detector pairs Q1 / RD1, Q2 / RD2 in Orbitalachsenrichtung OAR (or in the opposite direction ) can be effected.

A check of the completeness of the trajectories by means of simulations has shown that by means of the method according to the invention 100 a volume image VB can be generated, which has a data coverage of 100% along the entire volume and 5 cm from the isocenter and is thus comparable to conventional helix recordings. In contrast to conventional helix recording, this data coverage is given up to a distance of helix turns of 45 cm, which allows a shorter recording time and thus lower dose possible. In a conventional Helixaufnahme the distance of the Helixwindungen is 22.5 cm.

Here, a detector height DL became 30 cm, a source-to-detector distance SID of 1200 mm and a source-to-object distance SOD of 600 mm, the detector height DL being the width of the sensor surface SF1, SF2 in the direction of the orbital axis OA. This direction OA is usually referred to by the person skilled in the art as the v direction (if the detector is in portrait mode or in landscape mode, ie is not rotated about the beam axis).

The beam set is used to calculate the width h _{ISO of} a cone beam on the iso-axis IA, with which the sensor surface SF1, SF2 detects just over its entire detector height DL, as follows: h _ISO = DL SOD / SID.

Correspondingly, for the width w _{ISO of} a cone beam perpendicular to the iso-axis IA, which detects the sensor surface SF1, SF2 just over its entire width 2DH in the direction of rotation RR1, RR2: w _ISO = 2DH * SOD / SID (where DH is half the width of the sensor surface in rotation direction RR1, RR2). If it were not a short scan, all voxels on iso-axis IA are captured twice with a 360 ° rotation. This results in a maximum pitch of the helix segment-shaped trajectory BK1, BK2 of 2 · h _ISO. But this would only scanned half the volume to be reconstructed. For complete reconstructability, the maximum feed (slope) of the helical segmental trajectory BK1, BK2 must be corrected by the radius w _ISO / 2 of the volume as follows: P _helix = 2 · h _ISO - w _ISO / 2 = (2DL - DH) SOD / SID.

For the parameters used in the simulation, the maximum helical feed for SOD / SID = 0.5 is given by: P _helix ≈ 2 · 15cm - 20cm / 2 = 20cm.

With the chosen dimensions, the maximum feed P _{helix is} calculated to be 20 cm and not 22.5 cm, as determined in the numerical simulation. The deviation is not surprising since the above formula for P _{helix is} an estimate based on simplifications. The following feed can be selected for the proposed double helix: P _helix = 2P _helix .

With the present disclosure of the invention, a three-dimensional or four-dimensional volume image of an arbitrarily long volume can be generated for the first time by means of a C-arm angiography system. The acquisition takes place on zigzag-shaped trajectories, which are composed of helix-segment-shaped trajectory sections (BA1 or BA2), and which can be of any length in the orbital axis direction z. Thus, a three-dimensional volume image VB (without partial circulation artifact) can be generated by a normal-sized adult in one operation. This is not possible with known C-arm systems. Since the acquisition can be resorted to at least one non-reversing full helix Ha, Hb, all reconstruction methods (in particular all known and / or exact reconstruction methods) which are suitable for computer tomography can be used. This is especially true for spiral CT and helical CT procedures. In addition, optionally a recording time can be shortened, a dose efficiency can be improved and / or dual-energy methods can be used.

The invention relates to a tomography system R, which is prepared for the following: performing a first scan along a first helix-segment-shaped trajectory section BA1 and a second scan along a second helix-segment-shaped trajectory section BA2. In the first scan, a first data set DS1 and in the second scan a second data set DS2 is obtained and from the two data sets DS1, DS2 a fused three- or four-dimensional data set DS12 is generated, which is sufficiently complete for a reconstruction of a volume image VB without partial circulation artifact, while taken alone, both the first DS1 and the second DS2 data set for a reconstruction of a volume image VB without partial circulation artifact is too incomplete.

LIST OF REFERENCE NUMBERS

AF

exit area

AP1

minimum rotational angular position of the first helix segment-shaped trajectory section

AP2

minimum rotational angular position of the second helical segmental trajectory section

BA1

first helix segmental trajectory section

BA2

second helix segmental trajectory section

C1

first C-bow

C2

second C-bow

DH

half detector width in the direction of rotation

DL

Detector width in orbital axis direction

DR

Detector height in the direction of the axis of rotation

DS1

first record

DS2

second record

DS12

fused three- or four-dimensional dataset

EF

entry surface

Ha

first helix

hb

second helix

IA

Isoachse

MF

lateral surface

MP1

Center of the first detector

MP2

Center of the second detector

MSk

Mid-perpendicular of a short side of the sensor surface

MSg

Perpendicular to a long side of the sensor surface

MP2

Center of the second detector

OA

orbital axis

OAR

Orbital axis direction

PA

patient support

Q1

first beam source

Q2

second beam source

R

tomography system

RD1

first detector

RD2

second detector

RO

rotation

RR1

first direction of rotation

RR2

second direction of rotation

RS _C1

first rotation angle span

RS _C2

second rotation angle span

RV

completely reconstructable volume

RWD

Rotation angle difference

SB

ray beam

SF1

Sensor surface of the first detector

SF2

Sensor surface of the second detector

SID

Distance between the beam source and the sensor surface

SK1

Beam cone of the first beam source

SK2

Beam cone of the second beam source

SOD

Distance between the beam source and the object

SW

beam angle

T

period

u

Detector coordinate in the direction of rotation

v

Detector coordinate in orbital axis direction

VB

volume image

z

Orbital axis direction

ZR

cylinder radius

ZS

Central ray of the beam

100

method

110

Perform a first and a second scan

120

Gaining a first and a second record

130

Create a fused three- or four-dimensional data set

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102006040934 A1 [0005]

Claims (10)

 Tomography system (R), which is prepared to perform a first scan along a first helix segment-shaped trajectory section (BA1) and a second scan along a second helix segment trajectory section (BA2), wherein the tomography system (R) is prepared for a first scan during the first scan Record (DS1) and the second scan to win a second record (DS2) and to generate from the two data sets (DS1, DS2) a fused data set (DS12), which is for a reconstruction of a three- or four-dimensional volume image (VB) without Teilumlaufartefakt is sufficiently complete, in each case taken on their own both the first (DS1) and the second (DS2) data set for a reconstruction of a volume image (VB) without Teilumlaufartefakt is too incomplete. Tomography system (R) according to claim 1, characterized in that the first helix segment-shaped trajectory section (BA1) extends over a first rotation angle span (RS _C1 ) and the second helix segment trajectory section (BA2) extends over a second rotation angle span (RS _C2 ) Is the sum of the first (RS _C1 ) and the second (RS _C2 ) rotation angle span 360 °, wherein a minimum rotational angular position (AP2) of the second helix segmental trajectory section (BA2) against a minimum rotational angular position (AP1) of the first helical segment trajectory section (BA1) in the rotational direction (RR1, RR2) is offset by the first rotation angle span (RS _C1 ) or wherein the minimum rotational angular position (AP1) of the first helix segmental trajectory section (BA1) is opposite the minimum rotational angular position (AP2) of the second helical segment trajectory section (BA2) in the direction of rotation (RR 1 is arranged, RR2) about the second rotational angle range (RS _C2) was added. Tomography system (R) according to claim 1, characterized in that the first helix segment-shaped trajectory section (BA1) extends over a first rotation angle span (RS _C1 ) and the second helix segment trajectory section (BA2) extends over a second rotation angle span RS _C2 , wherein the first Rotation angle span RS _C1 is calculated as follows: RS _C1 = 180 ° + SW - RS _C2 , wherein the second rotation angle span (RS _C2 ) is at least half a width SW of a beam angle in the rotational direction (RR1, RR2), wherein a minimum rotational angular position (AP2) of the second helical segmental trajectory segment (BA2) is opposite a minimum rotational angular position (AP1) of the first helical segment-shaped trajectory section (BA1) is arranged offset in the rotational direction (RR1, RR2) by the first rotational angular span (RS _C1 ) or the minimum rotational angular position (AP1) of the first helix segment trajectory segment (BA1) compared to the minimum rotational angular position (AP2) of the second helical segment trajectory segment (BA1). BA2) in the rotational direction (RR1, RR2) is offset by the second rotation angle span (RS _C2 ). Tomography system (R) according to one of the preceding claims, characterized in that the tomography system (R) is prepared to obtain a first part of the second data set (DS2) with a second radiation spectrum which differs from a first radiation spectrum with which first part of the first data set (DS1) is obtained. Tomography system (R) according to one of the preceding claims, characterized in that the tomography system (R) is prepared to record the first data set (DS1) only on first helix segment-shaped trajectory sections (BA1), which extend in a first direction of rotation (RR1), and or to record the second data set (DS2) only on second helix-segment-shaped trajectory sections (BA2) which run in a direction of rotation (RR2) that is opposite or rectified to the first direction of rotation (RR1). Tomography system (R) according to one of the preceding claims, characterized in that the tomography system (R) is prepared to activate the first beam source (Q1) if a bisector (MSk, MSg) of a first sensor surface (SF1) of the first detector ( RD1) is aligned parallel to the first helix segment-shaped trajectory section (BA1), and / or to activate the second beam source (Q2) if a bisector (MSk, MSg) of a second sensor surface (SF2) of the second detector (RD2) is parallel to the second Helix segment-shaped trajectory section (BA2) is aligned. Tomography system (R) according to one of the preceding claims, characterized in that the tomography system (R) is prepared to the first Scan to perform when a center (MP1) of a sensor surface (SF1) of the first detector (RD1) relative to a central beam (ZS) of a beam (SB) of the first beam source (Q1) by half a detector width (DH) in the direction of rotation (RR1, RR2 ) or by a half detector width (DH) opposite to the direction of rotation (RR1, RR2) and / or that the tomography system (R) is prepared to perform the first scan when a midpoint (MP1) of a sensor surface (SF1) of the first detector (RD1) is shifted from a central beam (ZS) of a beam (SB) of the first beam source (Q1) by half a detector width (DH) in a direction of the first helix segment-shaped trajectory section (BA1). Tomography system (R) according to one of the preceding claims, characterized in that a minimum rotational angular position (AP2) of the second helix segment-shaped trajectory section (BA2) is spaced from a minimum rotational angular position (AP1) of the first helical segment trajectory section (BA1) in the orbital axis direction (z). Tomography system (R) according to one of the preceding claims, characterized in that the tomography system (R) for the first scan has a first beam source (Q1) and a first detector (RD1) associated with the first beam source (Q1), and for the second scan has a second beam source (Q2) and a second detector (RD2) associated with the second beam source (Q2). Procedure ( 100 ) for operating a tomography system (R), the method ( 100 ) comprises the following activities: - carrying out ( 110 ) a first scan along a first helix segment-shaped trajectory section (BA1) and a second scan along a second helix segment trajectory section (BA2); - Win ( 120 ) of a first data record (DS1) during the first scan and acquisition of a second data record (DS2) during the second scan, wherein both the first (DS1) and the second (DS2) data record for a reconstruction of a volume image (VB) are taken on their own without partial circulation artifact is too incomplete; and - generating ( 130 ) of a merged three- or four-dimensional data set (DS12) from the two data sets (DS1, DS2), which is sufficiently complete for a reconstruction of a volume image (VB) without a partial circulation artifact.

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